To answer both it is necessary to know two things: how far away certain galaxies are and how fast they are flying away from us (what is known as their recessional velocity).

为了回答这两个问题，首先必须知道两件：类星系我们有，们在以快的速度我们而去（即现在所谓的退行速度）。

To answer both, it is necessary to know two things—how far away certain galaxies are, and how fast they are flying away from us—what is known as their recessional velocity.

要回答这两个问题, 需要知道两件 - - 些星系我们有, 们我们飞行的速度有快 - - 也就是所谓的退行速度。